It is well known and conventional in the art to provide cigarettes and cigarette filters with means for introducing ventilating air into the cigarette for diluting the smoke stream. Such dilution of the smoke stream with air reduces the per puff quantity of particulate matter and gas phase components (e.g., CO and NO) contained in the cigarette smoke. It is likewise well known to employ a filter alone or in combination with air ventilation to further reduce the particulate matter in the smoke stream. Filtration does not, however, have any significant or measurable effect on the quantity of gas phase components in the smoke stream.
In general, filtration and air dilution also affect the pressure drop of a cigarette. Generally, filtration increases the pressure drop of the cigarette and air dilution decreases the pressure drop of the cigarette. Air dilution alone tends to reduce the pressure drop of an unfiltered cigarette to an unnacceptably low level. Accordingly, conventional cigarettes designed for low levels of particulate matter and gas phase components typically employ a combination of filtration and air dilution so as to provide an acceptable pressure drop along with the desired reduction in particulates and gas phase components.
It is also known to dilute unfiltered smoke with air to lower both the particulate matter and gas phase components of the smoke. For example, U.S. Pat. Nos. 4,393,885 and 4,585,015 disclose cigarette filters comprising a hollow coaxial tube through which all the smoke passes in an undiluted, unfiltered condition to the mouth end of the filter and an air pervious or porous cylindrical chamber surrounding the tube through which air passes to the mouth end of the filter where it is delivered with the undiluted, unfiltered smoke to the mouth of the smoker.
U.S. Pat. No. 4,506,683 discloses a ventilated mouthpiece for a smoking article comprising an air and smoke impervious core member having a plurality of smoke flow capillaries extending therethrough for delivering unfiltered smoke to the mouth end of the core member. Intermediate the length of the core member, ventilating air is introduced into a plenum chamber from which it passes through an axial channel to be commingled with the unfiltered smoke in a recess at the mouth end of the core.
U.S. Pat. Nos. 4,023,576; 4,380,241; 4,515,170; and 4,617,946 disclose mouthpieces for cigarettes in which unfiltered tobacco smoke is delivered to the mouth of the smoker and diluted with ventilating air at the mouth end of the mouthpiece at a point intermediate the ends of the mouthpiece.
It would be a desirable objective to provide a cigarette with the pressure drop characteristics of a conventional filtered cigarette and which has high air dilution so as to substantially reduce gas phase components to obtain a smoother smoke, yet has sufficiently high particulate matter in the smoke to provide the taste desired by the smoker.